Radiometric measurement

Abstract

A method of and apparatus for detecting a characteristic in particulate material wherein a stream of the material is caused to move past a plurality of detectors, each of which is responsive to the characteristic, the detectors being so arranged in relation to the material stream that the combined response of the detectors for a given particle possessing the characteristic is substantially independent of the position of the particle relative to the detectors as it passes the detectors.

We claim: 
     
       1. A method of detecting a characteristic in particulate material wherein a stream of the material is caused to move past a plurality of at least six detectors, each of which is responsive to the characteristic, the detectors being arranged transversely with at least three detectors above the material stream and at least three detectors below the material stream and arranged so that in each case at least two relatively large detectors are on opposing sides of at least one inner relatively smaller detector so that the combined response of the detectors for a given particle possessing the characteristic is substantially independent of the position of the particle relative to the detectors as it passes the detectors. 
     
     
       2. A method of monitoring the operation of a bulk ore sorter in which the reject fraction of the ore sorter is monitored using the method of claim 1 the reject fraction forming the said stream of material, and wherein an alarm condition is initiated when the combined detector response exceeds a predetermined reference value. 
     
     
       3. Apparatus for use with particulate material which includes a plurality of at least six detectors each of which is responsive to a characteristic in the material, and means for conveying the material past the detectors which are arranged transversely with at least three detectors above the conveying means and with at least three detectors below the conveying means and arranged so that in each case at least two relatively large detectors are on opposing sides of at least one inner relatively smaller detector so that the combined response of the detectors for a given particle possessing the characteristic is substantially independent of the position of the particle relative to the detectors as it passes the detectors. 
     
     
       4. Apparatus according to claim 3 in which the detectors are substantially simultaneously responsive to the characteristic in the given particle. 
     
     
       5. Apparatus according to claim 3 wherein the detectors and at least portion of the conveying means are located inside a shield. 
     
     
       6. Apparatus according to claim 3 in which the width of the conveying means is such that the material on the conveying means lies within a region wherein the combined detector response is uniform, the combined detector response efficiency decreasing outside the region. 
     
     
       7. An ore sorter which includes apparatus according to claim 3 and which includes a logic unit to which the combined detector response is applied which controls means for separating the ore stream into accept and reject fractions. 
     
     
       8. A monitor which includes apparatus according to claim 3 and which includes a logic unit to which the combined detector response is applied which initiates an alarm condition when the combined detector response exceeds a predetermined value. 
     
     
       9. Apparatus for use with particulate material which includes six detectors, each of which is responsive to a characteristic in the material, and means for conveying the material past the detectors which are arranged transversely with three detectors above the conveying means, and three detectors below the conveying means, arranged so that in each case two relatively large detectors are on opposed sides of an inner relatively smaller detector.